Telegraph repeaters



March 6, 1956 E. P. e. WRIGHT ETAL 2,737,544

TELEGRAPH REPEATERS 5 Sheets-Sheet 1 Filed March 15, 1953 Inventor E. P.G. WRIGHT- D. A. EI R f. Attorney March 1956 E. P. G. WRIGHT EIAL2,737,544

TELEGRAPH REPEATERS 5 Sheets-Sheet 2 Filed March 13, 1953 TIME SCALE srTSP 7/38 D. A.WElR.

S M j Inventor E. P G WRIGHT- SPA c5 A ttorney March 6, 1956 E. P. G.WRIGHT ETAL 2,737,544

TELEGRAPH REPEATERS 5 Sheets-Sheet 3 Filed March 13, 1953 OD EV SPACEMARK .lnventor E.P- G. WRI GHT D. A. WEIR 7 Attorney March 6, 1956 E. P.G. WRIGHT ETAL 2,737,544

TELEGRAPH REPEATERS Filed March 15, 1953 5 Sheets-Sheet 4 I l I I I I II T/ME SCALE I I I L J s7 F/ G .4.

r/3/ sp GZ/CQQ SPAC 90/ MARK I ,4 6/9 7/3 In ventor E. R G. WRIGHT D. A,w El R Attorney March 1956 E. P. G. WRIGHT ET'AL 2,737,544

TELEGRAPH REPEATERS 5 Sheets-Sheet 5 Filed March 13, 1953 T/ME SCALEF/GS.

SP F

SPACE v G/S Inventor E.R G.WR| GHT- A. WEIR Attorney.

United States Patent TELEGRAPH REPEATERS Esmond Phiiip Goodwin Wrightand Donald Adams Weir, London, England, assignors to InternationalStandard Electric Corporation, New York, N. Y.

Application March 13, 1953, Serial No. 342,124

, Claims priority, application Great Britain March 17, 1952 13 Claims.(Cl. 178-2) This invention relates to electric telegraph systems inwhich intelligence is conveyed in the form of signal combinations, eachcombination consisting of an invariable number of signal elements, andeach element being of two possible kinds.

The object of the invention is to increase the amount of intelligencewhich can be transmitted in a given period of time.

In is broadest aspect, the invention provides a telegraph systemcomprising means for transmitting combinations of elements of two kinds,each of which combinations consists only of a start element and aconstant number of intelligence elements, the start element of anysignal combination being always of opposite kind to that of the lastintelligence element of the immediately preceding combination.

It is to be understood that by the term intelligence elements are meantthe elements whose selection and arrangement vary according to thecharacter represented by the combination.

In the conventional start-stop teleprinter code, each signal combinationconsists of an invariable start element of one kind (e. g. space),(usually) five permutable intelligence elements of either kind and aninvariable stop element of opposite kind to the start element.

According to a second aspect of the invention there is provided atelegraph system comprising means for receiving combinations of elementsof two kinds, each of which combinations consists of invariable startand stop elements and a constant number of intelligence elements, whichsystem further comprises meansfor converting the received combinationsinto other combinations, each of which consists only of a start elementand a constant number of intelligence elements, the start element of anysig nal combination being always of opposite kind to that of the lastintelligence element of the immediately preceding combination, togetherwith means for transmitting the converted combinations.

According to a further aspect of the invention there is provided atelegraph system comprising means for receiv ing combinations ofelements of two kinds, each of which consists only of a start elementand a constant number of intelligence elements, the start element of anysignal combination being always of opposite kind to that of the lastintelligence element of the immediately preceding combination, whichsystem further comprises means for converting the received combinationsinto other combinations each of which consists of invariable start andstop elements and a constant number of intelligence elements, togetherwith means for transmitting the converted combinations.

Assuming the conversion is made from seven-element teleprinter codecombinations each having five intelligence elements, it becomes possibleto retransmit six-element combinations having the same five intelligenceelements, thus saving considerable transmission time.

Alternatively, seven-element signal combinations may be transmitted,each having six intelligence elements. The

additional intelligence element may be used to convey furtherinformation such as a case shift signal individual to each combination.On the other hand, as will be explained more fully later, the additionalelement may be used in connection with an error-checking system.

An embodiment of the invention together with various modificationsthereof will now be described with reference to the accompanyingdrawings of which:

Fig. 1 is a block schematic diagram of an electronic regenerativerepeater adapted to receive ordinary startstop seven-unit teleprintersignal combinations and to convert them into six-unit combinationscomprising a pseudostart signal element according to the invention,

Fig. 2 is a block schematic diagram of an electronic regenerativerepeater adapted to receive six-unit combinations comprising apseudo-start signal element according to the invention and to convertthem into ordinary startstop seven-unit teleprinter signal combinations,I

Fig. 3 shows a modification of the circuit of Fig. 1 adapted to add aseventh, error-checking code element to each transmitted combination,

Fig. 4 shows a modification of the circuit of Fig. 2

adapted to examine the seventh, error-checking code elesuitablereferences have been given to other specifications from which fullparticulars may be obtained. Thus, the drawings are functional in natureand are intended to show the processes involved rather than the actualmeans.

used.

The various symbols will be explained as they enter the description.

In this embodiment, the invention is applied to the typeof cold-cathoderegenerative repeater which forms the subject of the co-pendingapplication of V. J. Terry, D. S. Ridler, and D. A. Weir, filed March29, 1949, and bearing Serial No. 84,104.

Referring to Fig. 1 ordinary seven-unit start-stop teleprinter signalcombinations are supplied to the Mark and Space input leads shown in thelower part of 'the figure. They are examined by gates G1 and G2 at timesdetermined by examining pulsesapplied at point P+. These examiningpulses are of positive polarity and have a repetition frequency of fivekilocycles per second. Gates G1 and G2 each require two inputs beforethey can produce an output as denoted by the numeral 2 within the gatesymbol. A gate of this type is disclosed in the specification of BritishPatent No. 636,700 and its operation is there fully explained.

In the stop condition, marking potential is present on the line so thatpositive pulses are passed through gate G1 on to lead M.

When a start element is received, the opposite gate G2 conducts andpulses appear on lead S. These pulses pass to the start tube ST of atwo-condition device represented by the divided block F1. This devicemay conveniently comprise a pair of trigger tubes interconnected in Wellknown manner whereby the conduction of either tube effects theextinction of its partner. Normally the stop tube SP is fired but thefirst pulse from gate G2 changes over the condition of F1 by firing thestart tube ST.

The firing of the start tube of F1 causes a pulse to be passed to atwo-input gate G4. The other input to gate G4 comes from a fivekilocycles-per-second negative pulse source P synchronised with thesource of positive pulses P+. When gate G4 is energised from the starttube of F1, these negative pulses are passed to a time scale circuitcomprising three multi-gap gas-filled dischargetubesshown' as blocksCi,C2, and C3; and two further gas-filled trigger tubes shown as gatingdevices G and G6.- The time scale circuit is connected-and designed tooperate in the same manner as that shown and described in saidco-pending application. It s function is to count five-kilocyclenegative pulses applied at points marked P. As explained in the lastmentioned specification, C1 is arranged to count all the pulses, C2 tocount every tenth pulse and C3 to count every hundredth pulse. At anyparticular time after counting begins, a discharge will be presentacross aparticular gap in each tube, which gap will depend upon thenumber of pulses counted and hence upon the time that has elapsed. Thusafter, say, 175 pulses have been counted, gap 1 in the hundreds tube C3will be fired together with gap 7 in the tens tube C2 and gap 5 in theunits tube C1. Since there are five pulses every millisecond it will beapparent that the time interval which must elapse before theabove-condition can be reached is 175+5=35 milliseconds. In saidvco-pending application it is further explained and shown how thesimultaneous firing oftwo or three specific gaps in respective tubes maybe used to open a gating. circuit at a particular time.

In order to reduce the complexity of Figs. 1 and 2 of the present case,circuits for connecting the outputs of the counting tubes with variousgates' which are required to be opened at specific times have beenomitted but, instead, the times at which potentials are derived from thetimescale circuit are shown against various conductors connected togates thus: T1, 21, 41, etc. These figures are the time intervals inmilliseconds when counting tube outputs are obtained after the startingof the time scale circuit. In order to determine which gaps must befired at a particular time it is only necessary to multiply the time inmilliseconds by five. Thus at time T21, 105 pulses will have beencounted and the gaps fired will be gap 5 of C1, gap 0 of C2 and gap 1 ofC3.

The first action performed under the control of the time scale circuitis the transmission of the pseudostart element which, as has alreadybeen explained, is always arranged to be of opposite polarity to thestanding line condition at the end of the preceding element.

At milliseconds, an examining pulse from the time scale circuit isapplied to two examining gates G7 and G8 eachof which requires one otherinput. These other inputs are taken respectively from the space and marktubes of an output two-condition device F3 similar to F1.

If the output device F3 is in the space condition at 10 milliseconds (i.e. the last element of the previous combination was a space) the' gateG7 opens and applies a pulse to the mark lead which in turn changes overF3 to the mark condition.

If the output device F3 is in the mark condition at 10 milliseconds (i.e. the last element of the previous combination was a mark) the gate G8opens and applies a pulse to the space lead which in turn changes overF3 to the space condition.

It will be evident that the interconnection of gates G7 and G8 with theoutput device F3 is such that at 10 milliseconds the line conditions arealways reversed so inserting the pseudo-start element already referredto.

In regenerative repeaters it is' the invariable custom to examine eachof the seven elements of the incoming slgnal combinations in turn attheir respective centres. In the present case this examination isconfined to the five intelligence-bearing permutable elements. The ex-811111131101! is carriedout under the control of pulses derived at 30,50, 70, 90 and 110" milliseconds from thetime scale circuit and appliedto two-examining gates G11 and G12. Gate G11 opens: for a mark elementand passes a pulse forward-to fire the: mark tubeofoutput device F3.Similarly gate G12 opens for a space element and passes a pulse forwardto fire the space tube of F3.

At 138 milliseconds the stop tube SF of the twocondition device F1 isfired, so extinguishing the start tube ST and cutting off the supply ofpulses to the time scale circuit. At 138 milliseconds the number ofpulses which has been counted by the time scale circuit is l38 5=690.This means that a discharge is present across gaps t a and 6respectively of tubes C1, C2 and C3. It is thus necessary to reset onlytubes C2 and C3 to the initial condition i. e. with the discharge acrossgap 0 in either tube. This resetting is done by a transient voltagepulse produced (for example by reactive coupling) as F1 changes over. Inthe drawings, this transient output is differentiated from the otheroutputs by being shown as emanating from the end and not the sides ofthe block.

The output signal combinations from the device F3 will comprise thepseudo-start signal and five intelligencebearing permutable elements.These will be followed by an interval of at least. anotherelementsduration during which the polarity of the line will remain the same asthat of the last permutable element. At the end of this interval thenext psuedo-start element will arrive, of opposite. polarity to the lastpermutable element. Thus the interval between successive outgoingcombinations will be at least 140 milliseconds which is, of course, theminimum interval between successive incoming combinations. In order toeffect a saving in transmission time, the outgoing combinations may berecorded on a medium such as a magnetic tape. They can then bereproduced in such a manner that the above-mentioned interval iseliminated and each combination takes only milliseconds6 elementperiods-to transmit.

At the receivingstation it would be necessary to provide complementaryrecording and reproducing equipment so as to spread the signalcombinations out before converting them to ordinary seven-unitteleprinter code combinations each lasting for at least milliseconds.

In the embodiment being considered, it is assumed that the outputterminals of Fig. 1 are directly connected over a transmission circuitto the input terminals of Fig. 2.

The input circuit of Fig. 2 is similar to that of Fig. 1, the gates G14and G15 being respectively analogous to the gates G1 and G2. During amark signal, positive pulses appear on the mark lead M (via gate G14)and during a space signal, pulses from the same source appear on thespace lead S.

An output device F5, analogous to the device F3 in Fig. 1, comprises apair of tubes for spaces and marks and these provide respective inputsto. two gates G16 and GT7 which are provided to detect the pseudo-startelement. Gate G16 has another input connected to space tube S in thedevice F5 and gate G17 has an input connected to the mark tube of thesame device.

If the device F5 is left in the mark condition it means that the nextpseudo-start element will be a space and accordingly a second input isapplied to gate G17 thereby conditioning the. gate to detect it. If onthe other hand the pseudo-start signal is a mark after an interval ofspace it will be detected by the opposite gate G16.

Whichever of'thesev gates open, a pulse is passed to fire the start tubeST of a two-condition device F4. This acts in the same way as the deviceF1 in Fig. 1 and starts a time scale circuit of the same type as thatused in the circuit of Fig. 1.

At 10 milliseconds the space tube S of the output twocondition device F5is fired thereby forcibly inserting the invariable start element whichprecedes each teleprinter signal combination.

The five permutableelements of the received signal combinations areexamined in the usual manner by gates G19 and G20 (analogous to gatesG11 and G12 in Fig. 1) and the output device F conditioned accordingly.

At 130 milliseconds, the mark tube M of the output device F5 is firedthereby forcibly inserting the invariable stop signal which concludeseach teleprinter signal combination.

At 138 milliseconds the time scale circuit is stopped and reset in thesame manner as the time scale circuit of Fig. 1.

If a six-unit code is to be received over the line the input to F5 (Fig.2) at T130 is omitted and the input to F4 at T138 is changed to T118.The intelligencebearing elements are recorded, for example, on amagnetic tape recorder and the usual invariable start and stop elementsadded when the signals are reproduced.

It has already been explained that if seven-unit code combinations aretransmitted, each comprising a pseudostart element and five permutableelements, the remaining element may be used to provide a simpleerror-checking device. This can be achieved by modifying the circuits ofFigs. 1 and 2 as will now be described with reference to Figs. 3 to 5.In these latter figures, the items common to the earlier figures havebeen accorded the same references.

Briefly, the method of error-checking comprises the steps of countingthe number of space elements in each code combination (not counting thestart element), and inserting a space for the seventh element if thenumber of spaces is odd and a mark if the number of spaces is even. Atthe receiver a similar evaluation is made and the two check elements arecompared so as to see if an error has taken place.

Referring to Fig. 3, the space content of the incoming code combinationsis determined by a two-stage counting device C4 comprising (for example)two gas discharge gaps for registering odd and even totals respectively.At 2 milliseconds after the beginning of each cycle the device is resetin the even condition.

At 25, 45, 65, 85 and 105 milliseconds, the condition of the space leadS is examined by a gate G3 and these examination times occurrespectively during the five permutable elements of a code combination.The condition of C4 is reversed for each space element so that after theexamining pulse at 105 milliseconds, the device stands in the evencondition if there were no spaces or two or four spaces, and in the oddcondition if there were one, three (or five) spaces.

At 130 milliseconds, the condition of C4 is examined by a pair of gatesG-and G10. If C4 stands at odd, G9 opens to fire the output device F3into the space condition, while if C4 stands at even, G10 opens and F3is changed to mark, if not already at mark.

Thus the seventh element, inserted at 130 milliseconds indicates whetherthe five permutable elements of the combination comprised an odd or evennumber of spaces. Referring now to Fig. 4 which shows the modifiedreceiving side of the system, a space counter C5 is provided, controlledby an examining gate G13. The operation of the last two items is exactlysimilar to that of C4 and G3 already described in connection with Fig.3. Thus the space content of each received combination is recorded onC5.

If a received combination contains, for instance, an odd number ofspaces, then, the seventh element can be expected to be a space and thepseudo-start element of the succeeding combination should be a mark.Thus, if C5 is standing in the odd condition at the completion of areceiving cycle, as soon as pulses appear on the mark lead, a gate G21opens and starts the time scale circuit by firing F4 into the startcondition.

If on the other hand the preceding combination comprises an even numberof spaces, a gate G22 responds to the start transit from mark to spaceand starts the time scale circuit as before. 7

The presence of an error is detected by a two-condition device F2 having(for example) two discharge gaps one representing the error conditionand the other the no error condition. At five milliseconds after thestart of each cycle, this device is placed in the no error condition.

If a received combination has been found to have an odd number ofspaces, then when the seventh element arrives, the space counter C5 isstanding in the odd condition. The seventh element should then be aspace. At milliseconds, the condition of the mark lead is examined by agate G23 and if a mark is present (which should not be the case) gateG23 opens and changes over F2 into the error condition.

If the received combination contains an even number of spaces and theseventh element proves to be (wrongly) a space, then at 130milliseconds, a gate G24 opens and similarly changes over F2 into theerror condition.

The device F2 may, for example, control a contact marking relay so thatin the error condition a visual or aural alarm is given. The precisemeans for giving an indication of error are, however, immaterial to thepresent invention.

At 131 milliseconds, if an error has been assumed, a gate G18 opens andensures that the space counter C5 is reset in the even condition beforethe end of the receiving cycle.

The receiving arrangement of Fig. 4 suffers from the disadvantage thatany momentary transition from one line condition to the other will,during the rest condition be interpreted as a pseudo-start element. Thisrenders the receiver vulnerable to stray interference. In order to avoidthis, means may be provided to examine the line condition at someinterval (say 9 milliseconds) after the receipt of a supposedpseudo-start element and, if the line condition has changed back again,to stop the time scale circuit before any signal is sent out from thereceiver. A circuit for achieving this is shown in Fig. 5 which shouldbe considered with Fig. 4.

Let it be assumed that the number of spaces in the last combination wasodd, then the space counter C5 is set at odd, the incoming linecondition (assuming no error) is space and the receiving cycle willbegin as soon as a mark is received. At 9 milliseconds a gate G25examines the space lead and if the latter is now energised, signifyingthat the supposed start element was spurious, a pulse is passed to thestart-stop device F4 to place it again in the stop condition.

A gate G26 acts in a similar capacity if the start transition is frommark to space and the line has reverted to the mark condition by thetime 9 milliseconds has elapsed.

it will be apparent that in addition to providing a simple means ofchecking errors in reception, the arrangements described in connectionwith Figs. 3 to 5 provide a certain measure of security since amonitoring teleprinter would only start correctly when the start elementwas space and would be liable to start prematurely when the stopcondition was space. Thus a teleprinter connected to a line between thetransmitter and receiver would not be able to receive messagescorrectly.

While the principles of the invention have been described abo-ve inconnection with specific embodiments, and particular modificationsthereof, it is to be clearly understood that this description is madeonly by way of example and not as a limitation on the scope of theinvention.

What we claim is:

1. A telegraph system comprising means for continuously receivingcombinations of elements of two kinds, each of which combinationsconsists of invariable start and stop elements and a constant number ofintelligence elements, which system further comprises means forconverting the received combinations into other combinations, each ofwhich consists only of a start element and a constant number ofintelligence elements, the start element of any signal combination beingalways of opposite kind to that of the last intelligence element of the7 immediately preceding combination, together with means fortransmitting the converted combinations.

2. A telegraph system comprising means for continuously receivingcombinations of elements of two kinds, each of which consists only of astart element and a constant number of intelligence elements, the startelement of any signal combination being always of opposite kind to thatof the last intelligence element of the immediately precedingcombination, which system further comprises means for converting thereceived combinations into other combinations each of which consists ofinvariable start and stop elements and a constant number of intelligenceelements, together with means for transmitting the convertedcombinations.

3. A telegraph system as claimed in claim 1 in which means is providedfor converting the stop element of the received combination to anadditional intelligence element.

4. A telegraph system as claimed in claim 3 in which the additionalintelligence element is used to give a case shift indication.

5. A telegraph system as claimed in claim 3 in which the additionalintelligence element is used to indicate whether the total number of theremaining intelligence elements of one kind in the combination is evenor odd.

6. A telegraph system as claimed in claim 1 comprising means forregistering the last element or" a converted combination and meanscontrolled by the register during the invariable start element of thenext received combination for inserting into the corresponding convertedcombination a start element of opposite kind to that registered.

7. A telegraph system as claimed in claim 2 comprising means forregistering the last element of a received COlTr bination and meanscontrolled by the register during the start element ofthe next receivedcombination for initia ing the conversion and transmission of this nextreceived combination.

8. A telegraph system as claimed in claim 6 in which said register meanscomprises a two-condition device and in which said insertion meanscomprises a pair of gating devices cross-connected to said two-conditiondevice so that either gating device may only be rendered operative toinsert a start element of one kind when said two condition device is ina condition representing an element of the opposite kind.

9. A telegraph system as claimed in claim 7 in which said register meanscomprises a two-condition device and in which said initiating meanscomprises a pair of gating devices cross-connected to said two-conditiondevice so that either gating device may only be rendered operative is ina condition representing an element of the opposite" kind;

10. A telegraph system as claimed in claim 5 comprising a two-conditiondevice, means for registering by the concl.ion of said device whethersaid total number of elements of one kind is even or odd and a pair ofgating devices controlled by said two-condition device in such mannerthat either gating device may only be rendered operative to insert anadditional element of a respective kind when said two-condition deviceis in a respective one of its conditions.

11.. A- telegraph system as claimed in claim 2 in which the lastintelligence element of a received combination is used to indicatewhether the total number of the remaining intelligence elements is evenor odd, comprising means at the receiver for independently determiningWhether said total number is even or odd, means for comparing the resultof said determination with the last intelligence element as received,and'means for giving an error indication in the event of non-agreementresulting from said comparison.

12; A telegraph system as claimed in claim ll in which the result ofsaid determination is stored on a two-condition device, in which saidcomparison means comprises a pair of gating devices controlledrespectively by said two-condition device in its two-conditions andfurther controlled by the received signals during said last permutableel ment in such manner that one gating device will be operated if thedisagreement is of one kind and the other gating device will be operatedif the disagreement is of the other kind and in which saiderror-indicating device is arranged to be operated by either of saidgating devices.

1.3 A telegraph system as claimed in claim 9 comprisinga further pair ofgating devices controlled by said two-condition device, means forrendering one or other of said gating devices operative at a given timeafter the receipt of a start element to check that the start element isstill being received, and means operative if the start element has notpersisted, to prevent the initiation of the conversion operation.

References Cited in thefile of this patent UNITED STATES PATENTS

